Synchronizing Different Representations of Content

ABSTRACT

Two different representations of content are maintained, at least one of which is a composite representation of the content. The composite representation is multiple different components, each component stored as a separate file and each component including some of the data of the content. The composite representation also includes a manifest that identifies the various components. Different devices can edit the content, and access to the content is coordinated via a synchronization system. The synchronization system manages generation of one or more representations of the content. The synchronization system also manages synchronization of the different representations of the content, allowing changes made on various different computing devices to be reflected in the different representations of the content, and managing situations in which different computing devices may attempt to change the content concurrently.

CLAIM OF PRIORITY

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 14/550,769, filed Nov. 21, 2014, entitled“Synchronizing Different Representations of Content”, the entiredisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND

As computing technology has advanced and computers have becomeincreasingly commonplace, people have come to use their computers in avariety of different manners. One such use is editing images or othercontent on their computers. While users may enjoy the ability to editcontent on their computers, such editing is not without its problems.One such problem is that content can sometimes be very large in size,leading to situations in which some computers process the content veryslowly or cannot process the content at all, leading to user frustrationwith their devices.

SUMMARY

This Summary introduces a selection of concepts in a simplified formthat are further described below in the Detailed Description. As such,this Summary is not intended to identify essential features of theclaimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

In accordance with one or more aspects, a request for one or morecomponents of multiple components of a first representation of contentis received from a computing device. The first representation of thecontent comprises a composite representation of the content thatincludes the multiple components and a manifest identifying the multiplecomponents. A revision identifier identifying the first representationof the content is recorded, the first representation of the content anda second representation of the content being different representationsof the content. Based on the second representation of the content, thefirst representation of the content is generated, and a check is made asto whether the revision identifier identifying the second representationof the content changed during the generating of the first representationof the content. In response to the revision identifier remainingunchanged during the generating, the manifest is saved and the one ormore components are returned to the computing device.

In accordance with one or more aspects, a request including one or moremodified components of a first representation of content is receivedfrom a computing device. The first representation of content includesmultiple components and a manifest identifying the multiple components.A second representation of the content is re-constituted based on theone or more modified components, the first representation of the contentand the second representation of the content being differentrepresentations of the content. A check as to whether the secondrepresentation of the content has been modified since the firstrepresentation of the content was last generated is made. A previousversion of the second representation of the content is replaced with there-constituted second representation of the content only in response todetermining that the second representation of the content has not beenmodified since the first representation of the content was lastgenerated. A check as to whether the manifest has been modified duringthe re-constituting of the second representation of the content is alsomade. The first representation of the content is updated to include themanifest only in response to determining that the manifest has not beenmodified during the re-constituting of the second representation of thecontent.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different instances in thedescription and the figures may indicate similar or identical items.Entities represented in the figures may be indicative of one or moreentities and thus reference may be made interchangeably to single orplural forms of the entities in the discussion.

FIG. 1 illustrates an example system implementing the synchronizingdifferent representations of content in accordance with one or moreembodiments.

FIG. 2 illustrates an example of different representations of content inaccordance with one or more embodiments.

FIG. 3 illustrates another example of different representations ofcontent in accordance with one or more embodiments.

FIG. 4 illustrates an example synchronization system in accordance withone or more embodiments.

FIG. 5 is a flowchart illustrating an example process for maintainingsynchronization of different representations of content during a getoperation in accordance with one or more embodiments.

FIG. 6 is a flowchart illustrating an example process for maintainingsynchronization of different representations of content during a putoperation in accordance with one or more embodiments.

FIG. 7 illustrates an example system that includes an example computingdevice that is representative of one or more computing systems and/ordevices that may implement the various techniques described herein.

DETAILED DESCRIPTION

Synchronizing different representations of content is discussed herein.A representation of content refers to a manner in which the content isstored, including a number of files used to store the content and thedata stored in those one or more files. Two representations of contentare maintained, such as a single-file representation of the content anda composite representation of the content. The single-filerepresentation of the content is a single file that can be very large insize, such as on the order of Gigabytes, tens of Gigabytes, or more ofdata. The composite representation of the content is multiple differentcomponents, each stored as a separate file, and each including some ofthe data of the content. The composite representation also includes amanifest that identifies the various components. The components aretypically files that are smaller in size, such as on the order of tensor hundreds of Megabytes of data. Alternatively, the two representationsof content can be two different composite representations of the content(e.g., with different components including different data).

These different representations allow the content to be edited onmachines with different levels of resources (e.g., processing power,memory space, etc.). Computing devices with large amounts of resources(such as desktop computing devices) are able to manage editing of onerepresentation of the content (e.g., the single-file representation ofthe content). However, computing devices with smaller amounts ofresources (e.g., mobile devices such as smart phones or tabletcomputers) typically do not have the resources to manage editing of thatrepresentation of the content, and thus another representation of thecontent (e.g., the composite representation of the content) is used bysuch mobile devices, allowing the mobile devices to obtain and operateon the components of the content they desire.

The different devices editing content coordinate access to the contentvia a synchronization system. The synchronization system managesgeneration of one or more representations of the content. Thesynchronization system also manages synchronization of the differentrepresentations of the content, allowing changes made on variousdifferent computing devices to be reflected in the differentrepresentations of the content, and managing situations in whichdifferent computing devices may attempt to change the contentconcurrently.

FIG. 1 illustrates an example system 100 implementing the synchronizingdifferent representations of content in accordance with one or moreembodiments. The system 100 includes a full-resource or large-resourcecomputing device 102 with substantial memory and processor resources.The full-resource computing device 102 can be any of a variety ofdifferent types of computing devices, such as a desktop computer, aserver computer, a laptop computer, a game console, and so forth. Thesystem 100 also includes a low-resource device 104 with limited memoryand/or processing resources. The low-resource computing device 104 canbe any of a variety of different types of computing devices, such as anetbook computer, a tablet or notepad computer, a mobile station, anentertainment appliance, a set-top box communicatively coupled to adisplay device, a television or other display device, a cellular orother wireless phone (e.g., a smart phone), a handheld game console, anautomotive computer, and so forth.

The computing devices 102 and 104 each communicate with asynchronization system 106 via a network 108. The synchronization system106 is made up of any of a variety of different types of computingdevices, such as any one or more of the types of devices discussed withreference to computing devices 102 and 104. The synchronization system106 is typically made up of one or more full-resource computing devices.The network 108 can be any of a variety of different networks, such asthe Internet, a local area network (LAN), a phone network (e.g., acellular network), an intranet, other public and/or proprietarynetworks, combinations thereof, and so forth.

The synchronization system 106 includes a content store 110 that storesmultiple different representations of content. In one or moreembodiments, these representations include a single-file representationof the content and a composite representation of the content. A copy ofa single-file representation 112 of the content is communicated from thesynchronization system 106 to the full-resource computing device 102,allowing the full-resource computing device 102 to edit the contentusing the single-file representation of the content, and return a copyof the edited content to the synchronization system 106. Copies ofindividual components 114 of a composite representation of the contentare communicated from the synchronization system 106 to the low-resourcecomputing device 104, allowing the low-resource computing device 104 toedit the content using the composite representation of the content, andreturn copies of the modified components to the synchronization system106. The synchronization system 106 manages synchronizing changes to thedifferent representations of the content made by the computing devices102 and 104 as discussed in more detail below.

Alternatively, these different representations of content can includedifferent composite representations of the content. These differentcomposite representations can include, for example, different componentsfor different types of computing devices. For example, one compositerepresentation (representation A) of the content may include morecomponents than another composite representation (representation B), andrepresentation A can be used by full-resource computing devices andrepresentation B can be used by low-resource computing devices.

Reference is made herein to the full-resource and low-resource computingdevices referring to the memory and/or processing resources of thecomputing devices. The full-resource and low-resource computing devicescan also refer to the bandwidth or availability of a communicationchannel between a computing device and the synchronization system 106.For example, a communication channel may have low bandwidth (e.g.,capable of transferring 0.5-2 Megabytes per second), or may be desiredby a user of the computing device to be low usage (e.g., due to afinancial cost associated with transferring data over the communicationchannel). A computing device communicating via a communication channelhaving low bandwidth or low desired usage can also be referred to as alow-resource device (regardless of the memory and/or processingresources of the computing device).

FIG. 2 illustrates an example 200 of different representations ofcontent in accordance with one or more embodiments. The content can beany of a variety of different types of content, such as image or otherdrawing content, audio content, video content, text content,combinations thereof, and so forth. In the example 200, content 202 inthe form of an image or drawing is shown. The example 200 includes asingle-file representation 204 of the content 202 and a compositerepresentation 206 of the content 202. The single-file representation204 of the content 202 is a single file that includes the data of thecontent 202.

The composite representation 206 of the content 202 is a combination ofmultiple files, including multiple (x) component files 208(1), . . . ,208(x), and a composite representation manifest file 210. The manifestfile 210 identifies each of the component files 208 included in thecomposite representation 206. The component files 208 can be identifiedin different manners, such as by including in the manifest file 210 afile name of each of the component files 208.

The composite representation 206 is generated by transforming thesingle-file representation 204 into multiple components, and storingeach component as a component file 208. The transformation can beperformed in any of a variety of different manners depending on the typeof content 202. For example, image or drawing content 202 can be createdor edited using multiple different layers. The data for each of thesedifferent layers is stored in the single-file representation 204.However, the data for these different layers is transformed to adifferent component for the composite representation 206, each of thedifferent component files 208 storing the data for a different one ormore of the multiple layers.

By way of another example, video content can be made up of multipleframes, and can be created or edited using multiple different layers(that apply to one or more frames). Video content can be transformed bystoring data for different layers and/or different video frames asseparate component files 208. By way of yet another example, audiocontent can be made up of multiple audio segments (e.g., segments havingsome duration of time), and can be created or edited using multipledifferent layers (that apply to one or more audio segments). Audiocontent can be transformed by storing data for different layers and/ordifferent audio segments as separate component files 208.

FIG. 3 illustrates an example 300 of different representations ofcontent in accordance with one or more embodiments. In the example 300,content 202 in the form of an image or drawing is shown, although thecontent can be any of a variety of different types of content asdiscussed above. The example 300 includes two composite representationsof the content: composite representation 302 of the content 202 andcomposite representation 304 of the content 202.

The composite representation 302 of the content 202 is a combination ofmultiple files, including multiple (x) component files 308(1), . . . ,308(x), and a composite representation manifest file 310. The manifestfile 310 identifies each of the component files 308 included in thecomposite representation 302. The component files 308 can be identifiedin different manners, such as by including in the manifest file 310 afile name of each of the component files 308.

The composite representation 304 of the content 202 is a combination ofmultiple files, including multiple (y) component files 318(1), . . . ,318(y), and a composite representation manifest file 320. The manifestfile 320 identifies each of the component files 318 included in thecomposite representation 304. The component files 318 can be identifiedin different manners, such as by including in the manifest file 320 afile name of each of the component files 318. The values of x and y canbe the same or different, so the number of component files 308 in thecomposite representation 302 can be the same as or different than thenumber of component files 318 in the composite representation 304.

The different composite representations 302 and 304 of the content 202can be generated in different manners, based on programs that use thecontent 202. For example, an image editing program may have twoversions—one version for full-resource computing devices and anotherversion for low-resource devices. The composite representation 302 caninclude all of the data for the content 202, and the compositerepresentation 302 can be used by full-resource computing devices. Thecomposite representation 304 can include less than all of the data forthe content 202 (e.g., data to allow operation of the majority ofediting actions users typically desire to perform on a low-resourcedevice, but not data to allow operation for all of the editing actionsusers can perform on a full-resource device), and the compositerepresentation 304 can be used by low-resource computing devices.

The composite representation 304 is generated by transforming thecomposite representation 302 into the appropriate multiple components,and storing each component as a component file 318. The transformationcan be performed in any of a variety of different manners depending onthe type of content 202 and the programs that use the content 202. Forexample, transforming the composite representation 302 can includeexcluding from the composite representation 304 components that supportfunctionality not supported by low-resource devices.

Although two different representations of content are illustrated ineach of FIGS. 2 and 3, it should be noted that the techniques discussedherein are not limited to only two representations of content. Rather,the techniques discussed herein can be used analogously to synchronizeany number of different representations of content.

FIG. 4 illustrates an example synchronization system 106 in accordancewith one or more embodiments. The synchronization system 106 includesthe content store 110, a communication module 406, a get synchronizationmodule 408, a put synchronization module 410, and a transformationmodule 412. Although particular functionality is discussed herein withreference to particular modules, it should be noted that thefunctionality of individual modules discussed herein can be separatedinto multiple modules, and/or at least some functionality of multiplemodules discussed herein can be combined into a single module.

The content store 110 stores two representations of content, illustratedas representation A 402 and representation B 404. In one or moreembodiments, representation A 402 is a single-file representation of thecontent (e.g., a single-file representation 204 of FIG. 2) andrepresentation B 404 is a composite representation of the content (e.g.,a composite representation 206 of FIG. 2). Alternatively, representationA 402 is a composite representation of the content (e.g., a compositerepresentation 302 of FIG. 3) and representation B 404 is a compositerepresentation of the content (e.g., a composite representation 304 ofFIG. 3). Although only two representations 402 and 404 are illustratedin FIG. 4, it should be noted that the content store 110 can storemultiple representations for each of multiple different contents.

The communication module 406 manages communication between thesynchronization system 106 and various computing devices (e.g.,computing devices 102 and 104 of FIG. 1). This communication includessending representations (or components of representations) of content tocomputing devices, receiving representations (or components ofrepresentations) of content from computing devices, receiving requestsfor content from computing devices, and so forth.

The get synchronization module 408 manages the generation of compositerepresentations of content. The get synchronization module 408 alsofacilitates maintaining synchronization across the differentrepresentations of the content in response to requests for components ofthe composite representation (also referred to as get requests oroperations). In one or more embodiments, the get synchronization module408 exposes an interface (e.g., an application programming interface(API)) that is invoked by a computing device (e.g., computing device 104of FIG. 1) in order to obtain one or more components of a compositerepresentation of content. The interface can include various parameters,such as an identification of the particular content, an indication ofwhich components of the content are desired, and so forth.

The put synchronization module 410 manages the re-constitution orre-generation of one representation of content (e.g., a single-filerepresentation of content) based on received components of anotherrepresentation of content (e.g., a composite representation of content).Components of representation B of the content can be modified by alow-resource device and the modified components provided to the putsynchronization module 410. The put synchronization module 410 managesre-constitution of the representation A of the content to include thesemodified components. The put synchronization module 410 also facilitatesmaintaining synchronization across the different representations of thecontent in response to receipt of components of the compositerepresentation (also referred to as put requests or operations).

In one or more embodiments, the put synchronization module 410 exposesan interface (e.g., an API) that is invoked by a computing device (e.g.,computing device 104 of FIG. 1) in order to provide one or morecomponents of a composite representation of content to thesynchronization system 106. The interface can include variousparameters, such as an identification of the particular content, themodified components of the content, and so forth.

The transformation module 412 manages transformation of onerepresentation of content into another representation of the content.This transformation can be performed in various manners as discussedabove. The files generated by the transformation module 412 are saved inthe content store 110.

The get synchronization module 408 and the put synchronization module410 facilitate maintaining synchronization across the differentrepresentations of the content using an optimistic concurrency controlmechanism. Generally, the optimistic concurrency control mechanismallows the synchronization system 106 to proceed with processingrequests (e.g., get and put operations) from computing devices assumingthat there is no synchronization problem with performing the requests,and then verifies that no such synchronization problem in fact occurred.This allows the synchronization system 106 to avoid creating, clearing,and otherwise managing locks on files or other data.

The synchronization system 106 also uses identifiers of versions offiles, which can be referred to as revision identifiers. A revisionidentifier allows different files to be distinguished from one another,and different versions of a file to be distinguished from one another.Each time a change is made to a file and the file is saved, the savedfiled is a new version of the file and the revision identifier changes.The revision identifier can be generated in any of a variety ofdifferent manners that allow different versions of the file to beidentified. For example, the revision identifier can be generated byapplying a hash function to the file (e.g., a cryptographic hashfunction, such as any of the Secure Hash Algorithm (SHA) functions, suchas SHA-1, SHA-2, or SHA-3). In one or more embodiments, the revisionidentifier is an entity tag, although other identifiers canalternatively be used.

The revision identifiers allow the synchronization system 106 to verifywhether a change has occurred to a file over some time span. Forexample, components of a composite representation can be provided to acomputing device 104, which may modify the components and return themodified components to the synchronization system 106. Thesynchronization system 106 can determine whether the single-filerepresentation of the content was changed while the computing device 104had the components by comparing the revision identifier of thesingle-file representation at the time the components were sent to thecomputing device 104 to the revision identifier of the single-filerepresentation at the time the modified components were received fromthe computing device 104. If the revision identifiers of the single-filerepresentation at these two times are the same, then the synchronizationsystem 106 knows the single-file representation was not changed whilethe computing device 104 had the components.

Revision identifiers are assigned to a single-file representation ofcontent (e.g., single-file representation 204 of FIG. 2) as well as themanifest file of a composite representation of content (e.g., manifestfile 210 of FIG. 2, manifest file 310 of FIG. 3, manifest file 320 ofFIG. 3). The individual component files (e.g., component files 208 ofFIG. 2, component files 308 or 318 of FIG. 3) are identified by amanifest file of the composite representation, and thus the individualcomponent files do not need revision identifiers. These revisionidentifiers and their use are discussed in more detail below.

FIG. 5 is a flowchart illustrating an example process 500 formaintaining synchronization of different representations of contentduring a get operation in accordance with one or more embodiments.Process 500 is carried out by a synchronization system, such assynchronization system 106 of FIG. 1, and can be implemented insoftware, firmware, hardware, or combinations thereof. Process 500 isshown as a set of acts and is not limited to the order shown forperforming the operations of the various acts. Process 500 is an exampleprocess for maintaining synchronization of different representations ofcontent during a get operation; additional discussions of maintainingsynchronization of different representations of content during a getoperation are included herein with reference to different figures.

In process 500, a request for content is received from a computingdevice (act 502). The request, a get request or a request for a getoperation, includes an indication of one representation (e.g., asingle-file representation) of the content, an indication of a compositerepresentation of the content, and an indication of one or morecomponents of the composite representation of the content. The programon the computing device is configured with (or otherwise obtains)knowledge of the different components of content in the compositerepresentation, and provides an indication of the components of thecomposite representation used to perform a desired operation. Forexample, if a user desires to crop an image, components used to crop theimage can be requested by the program, or an indication that imagecropping is desired can be provided as part of the request and thesynchronization system implementing process 500 can determine thecomponents used to perform the image cropping operation.

The correspondence of the multiple representations of the content to oneanother is verified (act 504). The synchronization system implementingprocess 500 verifies that the indicated representations of the contentcorrespond to one another. For example, if the request identifies asingle-file representation of the content and a composite representationof the component, the synchronization system verifies that thesingle-file representation and composite representation arerepresentations of the same content. The synchronization system canmaintain an indication of which representations correspond to oneanother in any of a variety of manners, such as identifiers included inthe representations themselves, a separate list or record ofcorresponding representations, and so forth. If the verification fails,then process 500 ends and the synchronization system performs anappropriate recovery operation (e.g., informing the user that theoperation cannot be completed).

A check is made as to whether a particular representation (e.g., thesingle-file representation, or another composite representation) of thecontent has been modified since the requested composite representationwas generated (act 506). This particular representation of the contentis a representation of the content different from the requestedcomposite representation and with which the requested compositerepresentation is synchronized. The composite representation can havebeen generated by the transformation module of the synchronizationsystem in various manners, as discussed above. In one or moreembodiments, this check in act 506 is made based on the revisionidentifier of the particular representation of the content. The manifestfile of the composite representation includes the revision identifier ofthe particular representation of the content at the time the compositerepresentation was generated. If the revision identifier of theparticular representation of the content is the same as the revisionidentifier in the composite representation, then the particularrepresentation has not been modified since the composite representationwas generated. However, if the revision identifier of the particularrepresentation of the content is different than the revision identifierin the composite representation, then the particular representation hasbeen modified since the composite representation was generated.

If the particular representation is unmodified since the compositerepresentation was generated, then the synchronization system uses thepreviously generated composite representation (act 508), and returns therequested components form the previously generated compositerepresentation to the requesting computing device (act 510). There is noneed to re-generate the composite representation because the particularrepresentation has not been modified since generation of the previouscomposite representation, so the generation is bypassed in act 508. Thecomposite representation could alternatively be re-generated, althoughthe re-generated composite representation would have the same componentsincluding the same data as the previously generated compositerepresentation.

However, if the particular representation has been modified sincegeneration of the previous composite representation, then a revisionidentifier of the composite representation is recorded (act 512). Thisrecord of the revision identifier is used to maintain synchronizationbetween the different representations of content, as discussed in moredetail below.

A composite representation of the content is generated based on theparticular representation (act 514). The composite representation can begenerated by using the previously generated composite representation asa base or starting point, and then modifying (adding to and removingfrom) the previously generated composite representation as appropriate.

In one or more embodiments, the manifest for the compositerepresentation identifies each component file included in the compositerepresentation. These identifiers can include indications of when thecomponent file was created (e.g., a timestamp) or other identifier ofparticular versions of the component file (e.g., revision identifiers).The transformation module of the synchronization system generates thecomposite representation, and for each component the transformationmodule determines whether the data in component has changed since thepreviously generated composite representation was generated. If thecomponent has been changed, then the composite representation is changedto include the changed component. However, if the component has not beenchanged, then the composite representation keeps the previouslygenerated component.

This determination of whether the data in a component has changed sincegeneration of the previous composite representation can be made in anyof a variety of different manners, such as by comparing the component inthe previously generated composite representation to a newly generatedversion of the component. If the two components are the same then thedata in the component has not changed since generation of the previouscomposite representation. The component in the previously generatedcomposite representation can be compared to the newly generated versionof the component in different manners, such as by generating hash valuesfor each component and determining whether the hash values are the same.The hash values can be generated by applying a hash function to the file(e.g., a cryptographic hash function, such as any of Message-digest (MD)algorithms, such as MD5 or MD4).

Keeping previously generated components that have not been changed inthe composite representation can improve performance of the computingdevices receiving the components. A computing device can cache orotherwise have local copies of the components due to the user editing orhaving previously edited the content on the computing device. Thecomputing device can check the manifest of the composite representation,and if the computing device already has a local copy that is the sameversion as identified in the manifest, the computing device need notre-request the component from the synchronization system. If thecomponent were to be re-generated as part of the compositerepresentation however, the new version of the component would beidentified in the manifest, and the computing device would request thecomponent as the computing device knows (based on the manifest) that thecomputing device does not have the most recent version of the component.Thus, by not re-generating the component that has not been changed, thecomputing device can avoid the time and bandwidth usage of obtaining acomponent of which the computing device already has a copy.

Alternatively, each component can be generated and included as part ofthe composite representation in act 514. In such alternatives, eachcomponent is included in the newly generated composite representation,and identified in the manifest of the composite representation,regardless of whether the component has been changed since generation ofthe previous composite representation.

Additionally, references in the manifest to any components that are nolonger in the composite representation are deleted (act 516). Situationscan arise in which the particular representation is edited in a mannerthat results in a particular component no longer being generated. Forexample, a particular layer may be deleted from a single-filerepresentation of the content, and thus when generating the compositerepresentation a component for that layer is no longer generated. Insituations in which the composite representation is generated bymodifying the previously generated composite representation, indicationsof (and any other references to) a component that is no longer generatedare deleted from the composite representation.

A check is made as to whether the revision identifier of the compositerepresentation has changed since the composite representation generationbegan (act 518). This check is made by checking whether the revisionidentifier as recorded in act 512 is the same as the current revisionidentifier of the composite representation. If the revision identifierof the composite representation has changed since the compositerepresentation generation began, then process 500 returns to act 512.Situations can arise in which the composite representation of contentchanges during the composite representation generation of process 500.Given the change, the synchronization system cannot rely on thecomponents in the composite representation generated in acts 514 and 516accurately reflecting the data in the particular representation.Accordingly, if the revision identifier of the composite representationhas changed since the composite representation generation began, thenthe process 500 fails (act 520). To maintain synchronization across thevarious computing devices, the manifest for the composite representationbeing generated is not saved. The process 500 can optionally be repeatedin response to another get request.

However, if the revision identifier of the composite representation hasnot changed since the composite representation generation began, thenthe manifest for the newly generated composite representation is saved(act 522). The manifest is saved, for example, in the content store 110.The saving of the manifest includes generating a new revision identifierfor the manifest, as discussed above. The requested components are alsoreturned to the requesting computing device (act 510).

It should be noted that the generation of the composite representationand the manifest in acts 514 and 516 can be performed using temporaryfiles, and those files are not used by the synchronization system as thecurrent composite representation of the content until the manifest issaved in act 522.

FIG. 6 is a flowchart illustrating an example process 600 formaintaining synchronization of different representations of contentduring a put operation in accordance with one or more embodiments.Process 600 is carried out by a synchronization system, such assynchronization system 106 of FIG. 1, and can be implemented insoftware, firmware, hardware, or combinations thereof. Process 600 isshown as a set of acts and is not limited to the order shown forperforming the operations of the various acts. Process 600 is an exampleprocess for maintaining synchronization of different representations ofcontent during a put operation; additional discussions of maintainingsynchronization of different representations of content during a putoperation are included herein with reference to different figures.

In process 600, a put request and one or more modified components of acomposite representation of content are received from a computing device(act 602). These one or more components are modified, for example, inresponse to content editing operations performed by a user of thecomputing device at the computing device.

For the manifest used by the computing device, the copy of the manifestat the synchronization system is verified as being unmodified sincebeing sent to the computing device (act 604). The verification in act604 refers to the copy of manifest stored at the synchronization system(the manifest in the content store) rather than the copy of the manifeststored at or received from the computing device. This verification isperformed based on the revision identifier of the manifest. The putrequest received in act 602 includes an indication of the revisionidentifier of the manifest that the computing device has. If therevision identifier of the manifest that the computing device has is thesame as the revision identifier of the manifest of the compositerepresentation of the content at the synchronization system, then thecopy of the manifest stored at the synchronization system is unmodifiedsince being sent to the computing device. However, if the revisionidentifier of the manifest that the computing device has is differentthan the revision identifier of the manifest of the compositerepresentation of the content at the synchronization system, then thecopy of the manifest at the synchronization system has been modifiedsince being sent to the computing device. Such a change can occur, forexample, if another computing device is also editing components of thecomposite representation of the content.

If the manifest has been changed since being sent to the computingdevice, then the process 600 fails (act 606). To maintainsynchronization across the various computing devices, the compositerepresentation is not updated to reflect the received modifiedcomponents. Rather, the computing device performs another get operation(as discussed with reference to FIG. 5) to obtain the current compositerepresentation of the content, and edits are optionally re-made by theuser at the computing device. It should be noted that even though themanifest has changed, an individual component may not have changed. Thecomputing device can detect such situations (e.g., based on indicationsof when the component file was created or other identifiers ofparticular versions of the component file in the manifest), and if thecomponent has not been changed then repeat the put request (with therevision identifier of the manifest newly received by the computingdevice).

A check is made as to whether a particular representation (e.g., thesingle-file representation, or another composite representation) of thecontent has been modified since the requested composite representationwas sent to the computing device (act 608). This particularrepresentation of the content is a representation of the contentdifferent from the composite representation and with which the compositerepresentation is synchronized. In one or more embodiments, this checkin act 608 is made based on the revision identifier of the particularrepresentation of the content. An indication of the revision identifierof the particular representation of the content at the time thecomposite representation was previously sent to the computing device isreceived as part of receiving the put request in act 602 (e.g., themanifest file, which includes the revision identifier, can be receivedas part of receiving the put request in act 602). If the currentrevision identifier of the particular representation of the content isthe same as the revision identifier in the received manifest file, thenthe particular representation has not been modified since the compositerepresentation was sent to the computing device. However, if the currentrevision identifier of the particular representation of the content isdifferent than the revision identifier in the received manifest file,then the particular representation has been modified since the compositerepresentation was sent to the computing device.

If the particular representation has been modified since the compositerepresentation was sent to the computing device, then the process 600fails (act 606). To maintain synchronization across the variouscomputing devices, the composite representation is not updated toreflect the received modified components. Rather, the computing deviceperforms another get operation (as discussed with reference to FIG. 5)to obtain the current composite representation of the content, and editsare optionally re-made by the user at the computing device.

However, if the particular representation is unmodified since thecomposite representation was sent to the computing device, theparticular representation of the content is re-constituted based on thereceived modified components (act 610). The particular representationcan be re-constituted in various different manners by the transformationmodule. In one or more embodiments, a new composite representation isgenerated that includes the received modified components, and then eachcomponent in the new composite representation is read in by thetransformation module and the new particular representation of thecontent is generated. For example, all the components of the compositerepresentation can be read in by the transformation module, and a newsingle-file representation of the content is written out by thetransformation module.

Alternatively, the particular representation can be re-constituted inother manners. For example, the transformation module can read in theparticular representation of the content, and then modify the particularrepresentation of the content based on the modified components. Anychanges to the content reflected in the modified components are thusalso reflected in the particular representation of the content.

Situations can arise in which the particular representation of contentchanges since the composite representation was last generated (e.g., dueto user edits at another computing device), including during there-constituting of act 610. Accordingly, a check is made as to whetherthe particular representation of the content has been modified since thecomposite representation was last generated (act 612). This check ismade by checking whether the revision identifier indicated in the copyof the manifest stored at the synchronization system is the same as thecurrent revision identifier of the particular representation. If therevision identifier of the particular representation and the revisionidentifier indicated in the copy of the manifest stored at thesynchronization system are different, then the particular representationof the content has been modified since the composite representation waslast generated, and the process 600 fails (act 606). To maintainsynchronization across the various computing devices, the re-constitutedparticular representation does not replace the previous version of theparticular representation. Rather, the computing device performs anotherget operation (as discussed with reference to FIG. 5) to obtain thecurrent composite representation of the content, and edits areoptionally re-made by the user at the computing device.

However, if the revision identifier of the particular representation andthe revision identifier indicated in the copy of the manifest stored atthe synchronization system are the same, then the particularrepresentation of the content has not been modified since the compositerepresentation was last generated, and the re-constituted particularrepresentation replaces the previous version of the particularrepresentation (act 614). This replacing includes saving there-constituted particular representation as the particularrepresentation of the content (e.g., in the content store 110), andgenerating a new revision identifier for the particular representationof the content, as discussed above.

It should be noted that the generation of the re-constituted particularrepresentation in act 610 can be performed using a temporary file thatis not used by the synchronization system as the current particularrepresentation of the content until the re-constituted particularrepresentation replaces the previous version of the particularrepresentation in act 614. Thus, if a modified copy of the particularrepresentation of the content were received from another computingdevice during the re-constituting of the particular representation inact 610, that modified copy would replace the previous version of theparticular representation and would not affect the re-constitutedparticular representation.

Situations can also arise in which the composite representation of thecontent changes during the re-constituting of act 610 (e.g., due to useredits at another computing device). Accordingly, a check is made as towhether the manifest has been modified during the re-constituting of theparticular representation (act 616). This check is made by checkingwhether the revision identifier for the manifest as checked prior tostarting the re-constituting of act 610 (the revision identifierverified in act 604) is the same as the current revision identifier ofthe manifest of the composite representation. If the revision identifierof the manifest has changed since the re-constituting of the particularrepresentation began, then the manifest is dropped (act 618). Tomaintain synchronization across the various computing devices, theparticular representation of the content is given priority over thecomposite representation of the content. Accordingly, if the compositerepresentation and the particular representation of the content arechanged, the particular representation of the content gets priority andthe composite representation is dropped (e.g., deleted or otherwiseignored). However, the composite representation can be re-generated(e.g., in response to the next get request from a computing device).

However, if the manifest has not changed during the re-constituting ofthe particular representation, then the modified components in thecomposite representation of the content are saved (act 620). Ones of thecomponents of the composite representation are replaced with theirrespective modified components. The manifest is also saved, updated toidentify the re-constituted particular representation of the content(act 622). This updating includes saving the revision identifier of there-constituted particular representation (as generated in act 614) inthe manifest. The updating of the manifest (to include the revisionidentifier of the re-constituted particular representation, and themodified components) includes saving the manifest and generating a newrevision identifier for the manifest, as discussed above. The manifestand components of the composite representation are saved, for example,in the content store 110.

The techniques discussed herein support various usage scenarios.Multiple different representations of content, one or more of which maynot include data for all of the content, are made available by asynchronization system. A low-resource computing device can obtaincomponents of a composite representation of the content and allow a userof the low-resource computing device to edit the content on thelow-resource computing device, even though the low-resource computingdevice may not be able to edit other representations of the content(e.g., a single-file representation of the content). The low-resourcecomputing device can download only the components of the compositerepresentation that a program running on the low-resource computingdevice desires to perform actions requested by a user at thelow-resource computing device. The low-resource computing device canalso be running a smaller program, and need not support all of thecontent editing capabilities of other programs run on full-resourcecomputing devices.

The synchronization system maintains synchronization across thesedifferent representations of content using an optimistic concurrencycontrol mechanism. The synchronization system maintains synchronizationacross these different representations of content without imposing anysort of synchronization locks on files or forcing two multiple files tobe locked together.

It should also be noted that components of the composite representationcan be downloaded concurrently (in parallel). In some situations, thisdownloading of multiple components can be performed faster thandownloading of a single file including the multiple components. Thedownloading of only components desired by the program can also reducethe bandwidth use between the computing device and the synchronizationsystem, due to components not desired by the computing device not beingobtained by the computing device.

Various actions performed by various modules are discussed herein. Aparticular module discussed herein as performing an action includes thatparticular module itself performing the action, or alternatively thatparticular module invoking or otherwise accessing another component ormodule that performs the action (or performs the action in conjunctionwith that particular module). Thus, a particular module performing anaction includes that particular module itself performing the actionand/or another module invoked or otherwise accessed by that particularmodule performing the action.

FIG. 7 illustrates an example system generally at 700 that includes anexample computing device 702 that is representative of one or morecomputing systems and/or devices that may implement the varioustechniques described herein. This is illustrated through inclusion ofthe synchronization system 714, which may be configured tosynchronization different representations of content as discussedherein. Computing device 702 may be, for example, a server of a serviceprovider, a device associated with a client (e.g., a client device), anon-chip system, and/or any other suitable computing device or computingsystem.

The example computing device 702 as illustrated includes a processingsystem 704, one or more computer-readable media 706, and one or more I/Ointerfaces 708 that are communicatively coupled, one to another.Although not shown, computing device 702 may further include a systembus or other data and command transfer system that couples the variouscomponents, one to another. A system bus can include any one orcombination of different bus structures, such as a memory bus or memorycontroller, a peripheral bus, a universal serial bus, and/or a processoror local bus that utilizes any of a variety of bus architectures. Avariety of other examples are also contemplated, such as control anddata lines.

Processing system 704 is representative of functionality to perform oneor more operations using hardware. Accordingly, processing system 704 isillustrated as including hardware elements 710 that may be configured asprocessors, functional blocks, and so forth. This may includeimplementation in hardware as an application specific integrated circuitor other logic device formed using one or more semiconductors. Hardwareelements 710 are not limited by the materials from which they are formedor the processing mechanisms employed therein. For example, processorsmay be comprised of semiconductor(s) and/or transistors (e.g.,electronic integrated circuits (ICs)). In such a context,processor-executable instructions may be electronically-executableinstructions.

Computer-readable storage media 706 is illustrated as includingmemory/storage 712. Memory/storage 712 represents memory/storagecapacity associated with one or more computer-readable media.Memory/storage component 712 may include volatile media (such as randomaccess memory (RAM)) and/or nonvolatile media (such as read only memory(ROM), Flash memory, optical disks, magnetic disks, and so forth).Memory/storage component 712 may include fixed media (e.g., RAM, ROM, afixed hard drive, and so on) as well as removable media (e.g., Flashmemory, a removable hard drive, an optical disc, and so forth).Computer-readable media 706 may be configured in a variety of other waysas further described below.

Input/output interface(s) 708 are representative of functionality toallow a user to enter commands and information to computing device 702,and also allow information to be presented to the user and/or othercomponents or devices using various input/output devices. Examples ofinput devices include a keyboard, a cursor control device (e.g., amouse), a microphone, a scanner, touch functionality (e.g., capacitiveor other sensors that are configured to detect physical touch), a camera(e.g., which may employ visible or non-visible wavelengths such asinfrared frequencies to recognize movement as gestures that do notinvolve touch), and so forth. Examples of output devices include adisplay device (e.g., a monitor or projector), speakers, a printer, anetwork card, tactile-response device, and so forth. Thus, computingdevice 702 may be configured in a variety of ways as further describedbelow to support user interaction.

Various techniques may be described herein in the general context ofsoftware, hardware elements, or program modules. Generally, such modulesinclude routines, programs, objects, elements, components, datastructures, and so forth that perform particular tasks or implementparticular abstract data types. The terms “module,” “functionality,” and“component” as used herein generally represent software, firmware,hardware, or a combination thereof. The features of the techniquesdescribed herein are platform-independent, meaning that the techniquesmay be implemented on a variety of computing platforms having a varietyof processors.

An implementation of the described modules and techniques may be storedon or transmitted across some form of computer-readable media. Thecomputer-readable media may include a variety of media that may beaccessed by computing device 702. By way of example, and not limitation,computer-readable media may include “computer-readable storage media”and “computer-readable signal media.”

“Computer-readable storage media” refer to media and/or devices thatenable persistent and/or non-transitory storage of information incontrast to mere signal transmission, carrier waves, or signals per se.Thus, computer-readable storage media refers to non-signal bearingmedia. The computer-readable storage media includes hardware such asvolatile and non-volatile, removable and non-removable media and/orstorage devices implemented in a method or technology suitable forstorage of information such as computer readable instructions, datastructures, program modules, logic elements/circuits, or other data.Examples of computer-readable storage media may include, but are notlimited to, RAM, ROM, EEPROM, flash memory or other memory technology,CD-ROM, digital versatile disks (DVD) or other optical storage, harddisks, magnetic cassettes, magnetic tape, magnetic disk storage or othermagnetic storage devices, or other storage device, tangible media, orarticle of manufacture suitable to store the desired information andwhich may be accessed by a computer.

“Computer-readable signal media” may refer to a signal-bearing mediumthat is configured to transmit instructions to the hardware of thecomputing device 702, such as via a network. Signal media typically mayembody computer readable instructions, data structures, program modules,or other data in a modulated data signal, such as carrier waves, datasignals, or other transport mechanism. Signal media also include anyinformation delivery media. The term “modulated data signal” means asignal that has one or more of its characteristics set or changed insuch a manner as to encode information in the signal. By way of example,and not limitation, communication media include wired media such as awired network or direct-wired connection, and wireless media such asacoustic, RF, infrared, and other wireless media.

As previously described, hardware elements 710 and computer-readablemedia 706 are representative of modules, programmable device logicand/or fixed device logic implemented in a hardware form that may beemployed in some embodiments to implement at least some aspects of thetechniques described herein, such as to perform one or moreinstructions. Hardware may include components of an integrated circuitor on-chip system, an application-specific integrated circuit (ASIC), afield-programmable gate array (FPGA), a complex programmable logicdevice (CPLD), and other implementations in silicon or other hardware.In this context, hardware may operate as a processing device thatperforms program tasks defined by instructions and/or logic embodied bythe hardware as well as a hardware utilized to store instructions forexecution, e.g., the computer-readable storage media describedpreviously.

Combinations of the foregoing may also be employed to implement varioustechniques described herein. Accordingly, software, hardware, orexecutable modules may be implemented as one or more instructions and/orlogic embodied on some form of computer-readable storage media and/or byone or more hardware elements 710. Computing device 702 may beconfigured to implement particular instructions and/or functionscorresponding to the software and/or hardware modules. Accordingly,implementation of a module that is executable by computing device 702 assoftware may be achieved at least partially in hardware, e.g., throughuse of computer-readable storage media and/or hardware elements 710 ofprocessing system 704. The instructions and/or functions may beexecutable/operable by one or more articles of manufacture (for example,one or more computing devices 702 and/or processing systems 704) toimplement techniques, modules, and examples described herein.

The techniques described herein may be supported by variousconfigurations of computing device 702 and are not limited to thespecific examples of the techniques described herein. This functionalitymay also be implemented all or in part through use of a distributedsystem, such as over a “cloud” 720 via a platform 722 as describedbelow.

Cloud 720 includes and/or is representative of a platform 722 forresources 724. Platform 722 abstracts underlying functionality ofhardware (e.g., servers) and software resources of cloud 720. Resources724 may include applications and/or data that can be utilized whilecomputer processing is executed on servers that are remote fromcomputing device 702. Resources 724 can also include services providedover the Internet and/or through a subscriber network, such as acellular or Wi-Fi network.

Platform 722 may abstract resources and functions to connect computingdevice 702 with other computing devices. Platform 722 may also serve toabstract scaling of resources to provide a corresponding level of scaleto encountered demand for resources 724 that are implemented viaplatform 722. Accordingly, in an interconnected device embodiment,implementation of functionality described herein may be distributedthroughout system 700. For example, the functionality may be implementedin part on computing device 702 as well as via platform 722 thatabstracts the functionality of the cloud 720.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A method comprising: storing, by a computingdevice, a single-file representation of content and a compositerepresentation of the content that is different than the single-filerepresentation, the single-file representation including a plurality oflayers of the content, the composite representation including: aplurality of components including, respectively, different layers of theplurality of layers; and a manifest identifying the plurality ofcomponents; sending, by the computing device, the single-filerepresentation via the network to a different computing device;receiving, by the computing device, a modification to a layer of theplurality of layers of the single-file representation from the differentcomputing device; synchronizing, by the computing device, the pluralityof layers of the composite representation and the plurality of layers ofthe single-file representation based on the modification; receiving, bythe computing device, a request for a component including the layer fromthe plurality of components of the synchronized composite representationfrom another different computing device; sending, by the computingdevice, the component including the layer from the plurality ofcomponents of the synchronized composite representation to the anotherdifferent computing device responsive to receiving the request.
 2. Amethod as recited in claim 1, wherein the content is an image and theplurality of layers are layers of the image.
 3. A method as recited inclaim 1, wherein the content is a video and the plurality of layers arelayers of the video.
 4. A method as recited in claim 1, wherein eachcomponent of the plurality of components includes a respective layer ofthe plurality of layers.
 5. A method as recited in claim 4, furthercomprising receiving, by the computing device, a deletion of anotherlayer of the plurality of layers of the single-file representation fromthe different computing device, and wherein the synchronizing includesdeleting a component including the another layer.
 6. A method as recitedin claim 1, further comprising: in response to the compositerepresentation being modified since generation of the single-filerepresentation, the synchronizing including generating an updatedversion of the single-file representation based on the compositerepresentation.
 7. A method as recited in claim 1, the synchronizingincluding: using a previous version of the composite representation,including a previous version of the manifest, as a starting point; andreplacing, for each component that has changed since generation of theprevious version of the composite representation, the component in theprevious version of the composite representation with the changedcomponent.
 8. A method as recited in claim 1, the synchronizingincluding: using a previous version of the composite representation,including a previous version of the manifest, as a starting point; anddeleting, from the manifest, reference to a component included in theprevious version of the composite representation that is not included inthe composite representation.
 9. A method comprising: storing, by acomputing device, a single-file representation of content and acomposite representation of the content that is different than thesingle-file representation, the single-file representation including aplurality of layers of the content, the composite representationincluding: a plurality of components including, respectively, differentlayers of the plurality of layers; and a manifest identifying theplurality of components; receiving, by the computing device, amodification to a component including a layer of the plurality of layersof the composite representation from a different computing device;synchronizing, by the computing device, the plurality of layers of thecomposite representation and the plurality of layers of the single-filerepresentation based on the modification; receiving, by the computingdevice, a request for the single-file representation from anotherdifferent computing device; and sending, by the computing device, thesynchronized single-file representation including the layer to theanother different computing device responsive to receiving the request.10. A method as recited in claim 9, wherein the content is an image andthe plurality of layers are layers of the image.
 11. A method as recitedin claim 9, wherein the content is a video and the plurality of layersare layers of the video.
 12. A method as recited in claim 9, whereineach component of the plurality of components includes a respectivelayer of the plurality of layers.
 13. A method as recited in claim 12,further comprising receiving, by the computing device, a deletion of acomponent of the plurality of components, and wherein the synchronizingincludes deleting a layer included in the component.
 14. A method asrecited in claim 9, further comprising in response to the single-filerepresentation being modified since generation of the compositerepresentation, the synchronizing including generating an updatedversion of the composite representation based on the single-filerepresentation.
 15. A method as recited in claim 9, the synchronizingincluding: using a previous version of the single-file representation asa starting point; and replacing, for each layer that has changed sincegeneration of the previous version of the single-file representation,the layer in the previous version of the single-file representation withthe changed layer.
 16. A synchronization system implemented on one ormore computing devices, the synchronization system comprising: at leastone processor; a content store that stores a first representation ofcontent and a second representation of the content, the firstrepresentation of the content including multiple component files and amanifest identifying the multiple component files, the multiplecomponent files including, respectively, different layers of a pluralityof layers of the content, the second representation of the contentincluding the plurality of layers; and a synchronization module that,responsive to execution by the at least one processor, performsoperations including: receiving, from a computing device, a modificationto a layer of the plurality of layers of the second representation;synchronizing the plurality of layers of the first representation andthe plurality of layers of the second representation based on themodification; receiving, from another computing device, a request forone or more components of the multiple components of the firstrepresentation; and sending the one or more components of the firstrepresentation to the another computing device responsive to receivingthe request.
 17. A synchronization system as recited in claim 16,wherein the content is an image and the plurality of layers are layersof the image.
 18. A synchronization system as recited in claim 16,wherein the content is a video and the plurality of layers are layers ofthe video.
 19. A synchronization system as recited in claim 16, whereineach component of the plurality of components includes a respectivelayer of the plurality of layers.
 20. A synchronization system asrecited in claim 19, the operations further comprising receiving adeletion of another layer of the plurality of layers of the secondrepresentation from the computing device, and wherein the synchronizingincludes deleting a component including the another layer.